@abeyenen72
Just a question why are you using send an http request to SharePoint just to create an item?
You can directly use the action create item.
If there is a specific reason you are using send an http action then I would suggest you to research a little more how to run this action. I have not used this action much so exactly I don't know how this works. Hopefully someone else in the community might be able to help.
Or just simply use create item action if you can.
For others to help you just add screenshot of 400 error code you are getting in the send http request action.
And also add screenshot of your flow in edit mode so that people can see what exactly you are doing in the action. Hide the personal details.
